In previous work we obtained evidence for interaction between the enzyme carbamylphosphate synthetase and the enzyme ornithine transcarbamylase. We have now generated mutants which delete the gene coding for ornithine transcarbamylase and those which in addition delete the gene for aspartate transcarbamylase. At present we are studying the effect of the absence of these enzymes on the assembly and function of carbamylphosphate synthetase. We also established that RNA is an obligatory intermediate in the synthesis of the DNA precursor dCTP. This result was obtained from the analysis of double mutants, defective in cytidine monophosphate kinase and polynucleotide phosphorylase. We previously isolated a mutant of the cold sensitive type in the gene for nucleotide diphosphate kinase. This gene has now been roughly located in the vicinity of the gal-operon on the Salmonella typhimurium linkage map. From studies on the enzyme levels of nucleoside diphosphate kinase and pyruvate kinase under aerobic and anaerobic conditions it can be deduced that pyruvate kinase may play an important role as phosphorylating enzyme for nucleotides under anaerobic conditions; possibly replacing nucleotide diphosphate kinase. Mutants in the gene for deoxyuridine triphosphate pyrophosphatase (dUTPase) have been isolated by others in Escherichia coli; all mutants obtained so far are only partially defective. We set out to isolate deletion mutations in the gene for dUTPase. The project is in progress. BIBLIOGRAPHIC REFERENCES: Waleh, Nahid S. and J.L. Ingraham. 1976. Pyrimidine ribonucleotide monophosphokinase and the mode of RNA turnover in Bacillus subtilis. Archives of microbiology 110, 49-54. Abdelal, A.T.H., E. Griego and J.L. Ingraham. 1976. Arginine-sensitive phenotype of mutations in pyrA of Salmonella typhimurium: Role of ornithine carbamyltransferase in the assembly of mutant carbamylphosphate synthetase. Journal of Bacteriology 128, 105-113.